Description of device functions Proline Prowirl 73
146 Endress+Hauser
SELECT FLUID
(contd.)
Selected fluid: COMPRESSED AIR, ARGON, CARBON DIOXIDE, METHANE,
NATURAL GAS, NITROGEN, OXYGEN, GAS MIXTURE, REAL GAS
Applications:
For calculating the mass flow and the corrected volume flow of gases.
!
Note!
The process pressure (p) in the process pipe is required to calculate the process variables
and the measuring range limit values. The process pressure can be read in from an
external pressure measuring device (e.g. Cerabar-M, for details on wiring ä 27) via
the HART INPUT (ä 167), or can be entered as a fixed value in the OPERATING
PRESSURE function (ä 150).
Calculated variables:
The mass flow, the density and the corrected volume flow are calculated from the
measured volume flow, the measured temperature and the specified process pressure
using data saved in the measuring device.
!
Note!
• The NX-19 standard is suitable for natural gas at a specific density of between 0.554
and 0.75. The specific density describes the ratio between the reference density of the
natural gas to the reference density of air (ä 152).
• The AGA8, ISO 12213-2, SGERG-88 equation is suitable for pipeline-quality natural
gas with an appropriate make-up (ä 182).
Formulae for calculation:
• Mass flow: m = q · (T, p)
• Density (real gas): (T, p) =
ref
(p ÷ p
ref
) · (T
ref
÷ T) · (Z
ref
÷ Z)
• Corrected volume flow: q
ref
= q · ( (T, p) ÷
ref
)
m = Mass flow
q = Volume flow (measured)
q
ref
= Corrected volume flow
T = Operating temperature (measured)
T
ref
= Reference temperature (ä 151)
p = Process pressure (ä 150)
p
ref
= Reference pressure (ä 151)
= Density
ref
= Reference density (ä 152)*
Z = Operating Z-factor (ä 151)*
Z
ref
= Reference Z-factor (ä 153)*
* The values from the functions are only used if REAL GAS was selected in the SELECT
FLUID function (ä 143). In Prowirl 73, these values are always available for the other
gases.
(Continued on next page)
Function description, FLOW COMPUTER group
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